Pubben, U.S. Pat. No. 5,505,227, discloses a "hands free" system for controlling the flow of water to a faucet. The system includes a pilot valve which provides pilot water of controlled pressure to operate diaphragm valves in a control block. The valves in the control block may be respectively connected between hot and cold water supply lines and a faucet. The pilot valve may be located in a position where it can be operated by a user's knee, elbow or foot.
Key advantages of a system of this general type are that a user does not need to touch any valve by hand. Therefore such valves can be operated hygienically. For this reason, hands free valve systems have become widely used by health professionals such as dentists and doctors. Such systems also have the advantage that no electrical power or compressed air is needed for operation.
Although the Pubben system is very effective and has had significant commercial success there are some areas where it could usefully be improved. In particular, it has been observed that flow resonances may occur when the Pubben valve opens or closes. This can cause the system to make undesirable noises. Such resonances may continue for one second, or more, in some cases. The resonances can be exacerbated if the pilot valve has an intermediate position in which its output is simultaneously connected to both lower and higher pressure fluid supplies.
Further, the valve tends to close rather suddenly which precipitates water hammer. Water hammer is caused by the sudden stopping of a moving water column and results in high amplitude pressure waves which can bounce back and forth in plumbing pipes causing unpleasant noises and accelerating wear of the valve. After several years of use the wear caused by water hammer and valve resonances can cause the diaphragms in the valve block to become perforated, especially in their areas around the valve exit ports. Finally, the 3-way sliding spindle valves which are commonly used as pilot valves have seals which can wear undesirably rapidly.
Austin Jr. et al., U.S. Pat. No. 5,203,373 discloses another hands free faucet system. The Austin et al. system also uses pilot valves to control the flow of water through a pair of main valves. Austin Jr. et al. does not appear to provide any mechanism for reducing or eliminating water hammer and resonance effects. The inventors therefore are of the view that the Austin Jr. et al. valve system suffers from the same defects identified above.